Potentiometer



1966 H. M. FOX ETAL 3,266,004

POTENTIOME'TER Original Filed Spt. 50, 1963 INVENTORS HARVEY M. FOX WILLIAM ALFRED CFDSSLAND ATTORNEYS United States Patent 3,266,004 POTENTIOMETER Harvey M. Fox, 14 Stimson Ave, Lexington, Mass., and

William A. Crossland, Waltham, Mass; said Crossland assignor to said Fox Continuation of application Ser. No. 312,546, Sept. 30,

1963. This application May 20, 1965, Ser. No. 457,333

1 Claim. (Cl. 338-174) This application is a continuation of Serial No. 312,- 546, filed September 30, 1963 for Potentiometer, now abandoned.

The present invention relates to potentiometers and, more particularly, to a potentiometer wherein a conductive-plastic track is molded or otherwise formed as an integral part of a plastic insulating housing.

Potentiometers of the general type here involved have been built having a track, annular in shape, molded of a conductive plastic upon and slightly raised from the surface of a disc-shaped member. The member is thereafter mounted upon a shell housing with fine screws inserted into holes pre-drilled and tapped in the narrow peripheral edge of the disc-shaped member, with the track disposed within the housing. A shaft is journaled to the disc-shaped member and to the housing to carry contact means for removing a voltage from the track. It is necessary with this construction to form the apertures for receiving and mounting the potentiometer shaft in both the member and the housing prior to assembly thereof, and the positioning of these pre-formed apertures upon assembly to enable proper shaft alignment is often difiicult. In addition, the before-mentioned drilling and tapping of the track-carrying member has often resulted in splitting of the same; and alignment of the pre-drilled and tapped holes with holes in the housing to position the track orthogonal to the shaft also introd-uces serious difiiculties in assembly operations. Furthermore, since the track is molded on the surface of the disc-shaped member, it is unprotected and easily damaged or chipped in subsequent manufacturing and assembly steps.

An object of the present invention, accordingly, is to provide a novel potentiometer that eliminates the beforementioned problems of track positioning and alignment and, at the same time, obviates the need for the drilling and tapping.

Another object is to provide a potentiometer in which a track is molded upon a surface within the housing which thereafter protects the track from damage in the course of assembly and other manufacturing steps.

Still another object is to provide a novel and inexpensive potentiometer and the like.

Further objects will be evident in the description to follow and will be more particularly pointed out in connection with the appended claim.-

In summary, the objects of the invention are attained in a potentiometer assembly having a cylindrical insulating plastic housing provided with an integral wall closing off one end and open at the other end. A raised annular conductive-plastic track is molded upon the inner surface of the said integral end wall and a pair of electric terminals is connected to insulation-separated ends of the track, extending through the said integral end wall to permit external connection to a source of electric potential. A conductive surface is disposed at the center of the track and is connected through the said integral end wall to a further external terminal. A metal cover member is fitted to close 01f the said other end of the housing and has a tubular bearing-containing recess extending there-through, with a shaft from outside the cover through the recess along the axis of the cylindrical housing within 3,266,04 Patented August 9, 1966 ice,

the same, supported by the cover-recess bearings. The shaft carries near its inner end a pair of electrically connected conductive contactors insulated from the shaft and one of which extends radially from the shaft to engage and ride upon the raised track and the other of which brushes against the said integral end-wall conductive surface.

The invention will now be described in connection with the accompanying drawing, FIGURE 1 of which is an elevation view, partially cutaway, of a preferred embodiment of the invention; and

FIGURE 2 is a view taken upon the line 2-2 of FIG- URE 1 looking in the direction of the arrows.

Referring to FIGURE 1, a potentiometer assembly is shown having a cylindrical insulating plastic housing 1 provided with an integral bottom wall 2 closing off one end, the other or upper end of the housing being open to receive a cover member 3, as hereinafter discussed, which is preferably, though not always essentially, pressfitted into said other end. The housing 1 may be molded of an insulating plastic, such as a mineral-filled phenolic, and the cover member 3 is preferably fabricated of metal. The inner diameter of the housing 1 is step-bored to receive the cover 3. A flange 3' of the cover 3 is thereby secured to but slightly removed from the said other end to enable mounting of the potentiometer on a panel or the like.

An annular conductive-plastic track 4, as of well-known plastic-carbon mixtures and the like, is molded upon and slightly raised from the inner surface 2 of the integral bottom end wall 2. A pair of electric terminals 5 and 6 is provided, FIGURE 2, connected to insulation-separated ends of the track 4 and extending through the integral bottom wall 2 to external terminals 5' and 6', respectively, to permit external connection to a source of electric potential. The ends of the track may be separated by an insulating air gap, but it is preferred that an insulating portion 7 be integrally molded therebetween. Since the track 4 is molded integrally with the housing 1 it is always disposed in a plane orthogonal to the vertical walls of the housing 1 and to the later-described shaft 9 carrying the potentiometer contactor or slider 12. Also, the track, once molded, is protected against damage in subsequent manufacturing steps since it is disposed well within the housing 1.

The potentiometer shaft 9 extends from outside the cover 3 through a tubular bearing-containing recess therein and along the axis of the cylindrical housing 1 within the same, being rotatably supported solely by the coverrecess bearings and being secured therein against axial movement by a pair of lockingmembers 15 and 16 secured within annular depressions, not shown, in the shaft 9. The thickness of the cover 3 and thus the separation of the bearings in the recess is made sufficient to provide adequately stabilized support for the shaft.

The shaft 9 carries near its inner end a pair of elec trically connected conductive contactors 12 and 13, which are an integral part of a conductive ring 11 secured by rivets 11' to an insulator disc 14 that is fitted to the said inner end to rotate with the shaft 9. The contactor 12 extends radially from the shaft 9 and is bent downward resiliently to engage and ride upon the raised track 4. The contactor 13 is bent inwardly from the opposite side of the ring 11 to brush against a conductive surface 8 disposed in the end wall 2. The conductive surface 8 is shown at the center of the track 4 and is connected to a terminal 10' that extends through the integral end wall 2 to a further external terminal 10'.

Once a voltage has been connected across the external terminals 5 and 6', as before mentioned, a continuously variable output voltage may be withdrawn between, for

example, the terminal and the further terminal current passing from the track 4 through the said conductive member to the terminal 10'. The output voltage will be minimum when the contactor 12 is nearest the end of the track connected to the terminal 5 and will increase as the contactor 12 is moved in a counter-clockwise direction toward the terminal 6.

For the output voltage of the potentiometer to reflect positional changes of the contactor 12 in a predictable fashion, contact pressure between the contacts 12 and 13 and the track 4 and conductive surface 8, respectively, must be, constant as the shaft 9 is rotated. This necessitates that the shaft 9 be orthogonal to the upper surface of the track 4 and that the shaft be substantially concentric with the track. This is effected with facility with-in normal manufacturing tolerances by use of the construction herein disclosed and results in the production of an inexpensive potentiometer.

The conductive ring 11 may be made of beryllium copper for resilience and the contact surfaces of the contactors 12 and 1 3 may be plated at the contact surfaces there-of, for example, with platinum, silver or gold.

Modifications of the invention will occur to those skilled in the art and all such modifications are considered to be within the spirit and scope of the present invention as defined in the appended claim.

What is claimed is:

A potentiometer assembly having, in combination, a one-piece cylindrical insulating plastic housing having an integral wall closing off one end of the housing, the housing being open at the other end, a raised annular conductive-plastic track integrally molded upon the inner surface of said integral end wall ooaxially with said housing and having an exposed surface which lies in a plane orthogonal to the axis of said housing, said track having a pair of ends separated by insulation integrally molded thereto to produce a closed ring integral with said housing, the side wall of said housing extending from said integral end wall well beyond said track, thereby to shield said track from damage, a pair of electric terminals connected to said ends of the .track and extending through said integral end wall to permit external connection to a source of electric potential, a conductive surface disposed upon said inner surface of said integral end wall at the center of the track and connected through the said integral end wall to a further external terminal, a cover fitted to close off said other end of the housing, said cover being supported on an annular internal step of said side wall and having an annular flange spaced from the said other end of said housing when the cover is seated on said step to permit panel mounting of said potentiometer, said cover having a tubular bearing-containing recess extending therethrough :coaxially with said housing, a shaft extending from outside the cover through the recess along the axis of the cylindrical housing within the same and supported by the cover-recess bearings, said cover having a substantial thickness to stabilize said shaft, whereby orthogonality of the plane of the exposed surface of the track and said shaft is ensured, the shaft carrying near its inner end a pair of electrically connected conductive contactors one of which extends radially from the shaft to enagage and ride upon the exposed surface of the raised track and the other of which brushes against the said integral end wall conductive surface, said contactors comprising resilient integral arms of a conductive ring secured to an insulator disc fitted to the inner end of said shaft, the resilient arm of said one contactor and the resilient arm of said other contactor being bent from opposite ends of said conductive contactor ring, said one contactor arm extending radially away from the axis of said shaft and said other contactor arm extending radially toward said shaft axis.

References Cited by the Examiner UNITED STATES PATENTS 2,358,991 9/1944 Miller 338-164 2,700,719 1/1955 C0161 et al 338-174 2,885,519 5/1959 Louis et a1 338202 3,096,499 7/1963 Hudson et a1 338174X 3,105,949 10/1963 Zarrillo 338-174 FOREIGN PATENTS 1,297,417 5/1962 France.

883,559 11/1961 Great Britain.

ANTHONY BARTIS, Acting Primary Examiner. 

